Method of making cigarette filter



United States Patent 3,484,322 METHOD OF MAKING CIGARETTE FILTER George Esler Inskcep, Richmond, Va., assignor to Philip Morris Incorporated, New York, N.Y., a corporation of Virginia No Drawing. Filed Dec. 21, 1966, Ser. No. 603,426 Int. Cl. A24f 7/02; Bllld 29/08 US. Cl. 156292 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to an improved cigarette filter and method of making the same. More particularly, the invention relates to an improved active-adsorbent-containing filter and method of making the same.

In copending application Ser. No. 542,518, a method and apparatus are described for making tubular articles and, more particularly, for making a continuous cigarette filter stock which can be severed into sections of predetermined lengths for use in cigarette manufacturing machinery.

Of the essential criteria governing the manufacture of cigarettes, the primary consideration is that the methods and apparatus for manufacture must be readily suited for making large quantities of cigarettes rapidly, economically, and with consistent quality. To adhere to this criterion there have been devised for the tobacco industry in the past, cigarette making machines capable of producing many thousands of cigarettes per hour. This machinery and the cigarette filling, rolling and cutting techniques attendant therewith are fully satisfactory for the intended purposes. With the now commonplace use of filters in cigarettes it has become increasingly important that methods and apparatus employed for manufacturing the filter units be such that they are adapted readily to use with existing cigarette making methods and machinery. Furthermore, the filter itself has become the object of considerable development and may take various forms and include various filter compositions. Thus, as new types of filters evolve, it is, from a commercial or economic viewpoint, necessary to match these develop ments with appropriate methods and apparatus for continuous production of the filter units in the immense quantities involved.

The invention in the above-described application has for an object the provision of a method and apparatus for making tubular cigarette filter elements, more specifically, filter elements comprised of two interfitting semicylindrical shell portions having a strip of filter material supported longitudinally in the assembled shell portions. Another object of said invention is to provide a method and apparatus for making cigarette filters by thermoforming a relatively thin, continuous plastic strip in a continuous operation into shaped sections corresponding to the shell portions, the thermoforming being characterized by the fact that it involves a deep draw operation. The shaped sections are then assembled after a continuous strip of filter material is inserted in one, and the 3,484,322 Patented Dec. 16, 1969 assembly is sealed. Another object of said invention is to thermoform a continuous tubular article in a manner providing that the article may be easily severed into individual unit lengths without requiring finish trimming of the severed unit lengths.

The invention involved in the above-mentioned application is concerned with making in a continuous operation, a continuous stock of plastic cigarette filters of novel design. More specifically, each cigarette filter involved in said application comprises a tubular shell having a strip of filter material supported axially centrally therein with suitable barriers in the shell diverting smoke drawn therein in one or more courses through the filter strip. In accordance with the teaching of the invention, the cigarette filter elements may be made in a continuous operation by suitably shaping a continuous plastic strip into two longitudinal shell portions and thereafter slitting the strip to separate the two shell portions which are adapted to interfit one with the other so as to form a continuous tubular structure. The separated shell portions may thereafter be led through a series of devices which will properly orient the shell portions one with the other to facilitate eventual assembly, and which feed a strip of filter material therebetween before the shell portions are joined in assembled condition. Suitable means to seal the assembled shell portions are also provided as well as a device to impregnate and emboss spaced sections of the filter strip material before assembling the filter, the impregnated sections of the filter strip acting as antiwicking Zones to prevent migration of nicotine, tars etc. therethrough during smoking. The continuous filter assembly may thereafter be cut into smaller unit or plural unit lengths for further use in automatic cigarette making machinery wherein the filter unit is joined to the tobacco cylinder.

While the above-described filter provides an effective filtering medium for tobacco smoke, it has been found that such a filtering medium can be improved by the inclusion therein of granular active adsorbents, such as activated carbon particles. When such particles are employed in conjunction therewith, they can provide overall filtration which is extremely desirable, resulting in removal of undesirable portions of the gas phase of the tobacco smoke and in an improvement in mildness and flavor of the smoke.

It has been found, however, that certain particles cannot simply be included loosely in the filter structures described above, since they do not provide uniform filtration thereby. Furthermore, the particles cannot simply be included in the adsorbent material which is employed in the filter, since the end thereof would be exposed to the smokers view and would also contact the smokers tongue, with the possibility that some adsorbent, for example carbon particles, could be transferred to the smokers mouth.

The present invention overcomes the above-enumerated disadvantages and provides a superior .filter for tobacco smoke.

In accordance with the present invention, the continuous belt or strip employed in the filter described above is painted on one or both sides with an adhesive, as set forth below, and granular active adsorbent particles, for example activated carbon particles, are thereafter applied thereto to be held firmly in place on the strip by means of the adhesive. It may sometimes be feasible or preferable to apply the adhesive and carbon simultaneously, but this mode of operation will restrict the choice of adhesives to those which will not tend to coat the carbon and it will tend to restrict the carbon to the smaller particle sizes. The application of the adhesive may be by means of one or a pair of printing wheels having discontinuous lands of such area and spacing as to apply adhesive to only the areas desired, or by means of intermittent spray application from very close range, or by brush or sponge applicator or any of the means well known in the arts of printing, painting, or coating for the purpose of discontinuous application. For application of the carbon the strip may then be caused to come in contact with a bed of carbon particles or they may be dusted on the strip in such a manner that particles not adhering will fall off. The amount of carbon applied will be determined by the amount and nature of the adhesive and the area over which it is coated.

Reference may advantageously be made to the disclosure, including the drawings, of said copending application Ser. No. 542,518, which is helpful in understanding the present invention.

When the carbon and adhesive are mixed before application, applicators similar to those described for the ad hesive are usable, but the most generally operable is the printing wheel.

Belts or sheets which may be employed may be made of the following materials: Cellulose fibers, organic fibers or microfibers, foams, or similar porous materials. The filter element preferably should have a porosity of 38 seconds (determined by ASTM method D726-58 as modified by using 50 ounce cylinder with results obtained from 300 cc. in lieu of conversion to 100 cc.) a thickness of between 60-90 mils and a density of about O.20.4 gm./cc.

Activated carbon particles may be employed in the following forms and sizes: granules or dust, 8 mesh to finer than 325 mesh, preferably 12 to 200 mesh.

The adhesive which may be employed may be the following: aqueous latex adhesives, such as butadiene-styrene polymer latex, aqueous polyvinylpyrrolidone solution, polyvinyl alcohol solution, starch or dextrin suspension or solution, silicone greases, polyethylene oxides, cellulose derivatives such as methyl cellulose or carboxymethyl cellulose, or any adhesives known in the art as pressure-sensitive adhesives or like adhesives which retain tackiness for at least a short period after application so that the activated carbon or other desired granular material may be caused to adhere to the area covered by the adhesive.

The areas to be covered may be as follows: that area of the filter strip which will after assembly lie entirely within the filter shell or case and not at the point of contact of the strip with a barrier portion of the case. The area to be covered by the adhesive may be on one or both surfaces of the filter strip or some fraction of these surfaces. The adhesive, after drying if such is required, should not cover the filter surface in such a way as to block the surface appreciably to the flow of smoke but rather should leave the porosity of the filter subsiantially as it was before application.

Preferably, the areas covered are as follows: the entire area of the filter strip which will lie within the shell of the assembled filter and which is on the filter strip surface on the smoke exit side.

The amount of carbon employed is as follows: from about to 200 mg. per filter, preferably from 10 to 100 per filter.

The amount of adhesive employed is as follows: that amount which is the least which will hold the carbon particles in place, usually from 5 to 100% of the weight of the carbon. This will vary according to the particular adhesive employed and to the characteristics of the carbon, particularly its particle size.

The following examples are illustrative:

Example 1 Pads were cut from cellulose linters sheet to fit the two interfitting semi-cylindrical shell portions (each mm. length) described earlier in this application and each pad for a filter unit was waxed and compressed at the ends to the thickness required by the configuration of the case. The pad was then pressed into a thin layer of a silicone grease (Dow-Corning Corporation, highvacuum grease) so that the grease was applied to one face of the portion of the pad which would lie Within the case. The same face was then pressed into a bed of activated carbon (PCB coconut charcoal, 12 x 30 mesh, Pittsburgh Chemical Company). The average weight of carbon retained was 35 mg. per unit. Filters were assembled from these pads and attached to conventional commercial cigarette rods. When four of these cigarettes were smoked and the gas phase of the combined smoke was analyzed by a gas chromatographic technique which measures the organic compound content of each puff, the total delivery per cigarette was 4.9 mg. (in terms of benzene equivalent). The same cigarettes smoked without filters delivered 5.4 mg.

Example 2 Pads cut and compressed as in Example 1 were brushed on one face in the area to be located within the case with an aqueous latex (513 K butadiene-styrene copoly mer, Dow Chemical Company). The same'faces were then pressed on a bed of 12 x 30 mesh activated charcoal with the result that an average of 30 mg. of charcoal was retained by each pad. The pads were'incorporated into two 20 mm. shell portions as described above. Charcoal did not adhere to untreated areas.

Example 3 The apparatus described in copending application Ser.

(such as for example cellulose linters web), wax and emboss (compress) said strip of filter medium at longitudinal intervals, and finally to assemble said filter stripbetween said semi-cylindrical sections to produce a continuous tubular form of interconnected filter units.

The strip of filter medium, after its passage through the pair of printing rolls which apply a wax-like material and the pair of embossing rolls which compress the printed areas, is according to the present invention passed through a third pair of rolls which differ from the second pair only in being unheated and in the greater relative length of the lands or printing areas, which in the third rolls are of approximately the length of the interior section of the finished individual longitudinal-partition filters. This third pair of rolls is arranged to contact a supply of polyethylene glycol (Carbowax 600) so that a film of the resin is picked up by the lands. The rolls are so synchronized with the first two pairs of rolls that the resin is applied to the area between the waxed embossed spots on the filter strip. This moving strip then is conveyed from these rolls in a direction approximately 10" below the horizontal toward the assembler portion of the filter-making apparatus. Between the last rolls and the assembler, the strip is caused to pass through an enclosed chamber having openings for the entrance and exit of the strip; within the chamber is a bed of 48 x mesh activated carbon agitated so that some of the particles strike the under surface of the moving strip and become attached to the resin-treated portions. A quantity of the same type of carbon sufiicient to replenish that removed by the moving strip is caused to sift through a chute in the chamber directed toward the upper surface of the strip at a point above the agitated bed, 'so that a portion of the incoming carbon becomes attached to that surface and the remainder falls into the bed. The strip is sufficiently agitated by its own motion and that of the bed that carbon particles not in contact with resin will fall from the strip. The strip then passes to the conveyerassembler section where it becomes sandwiched between the two converging shell portions to form a continuous tube of successive filter sections as described in the above-mentioned application Ser. No. 542,518. The amount of resin applied to each surface of each filter strip unit is about 2 mg. and the total amount of carbon per filter unit is about 50 mg. The assembled filter tube is cut into 80 mm. lengths made up of four filter units and these lengths are supplied to a cigarette assembler to be cut and attached to tobacco rods in the conventional manner.

In one embodiment of this invention, the path of the filter strip 22 as shown in copending application Ser.

No. 542,518, in FIGURE 26, through the pairs of rolls 207-208 and 215-216 leads next to a pair of rolls similar to 215-216 but having lands contacting (but not significantly compressing) the areas between the waxed embossed areas prepared by the two pairs of rolls pictured, that is, the upper and lower surfaces of the uncompressed areas of the strip 22 shown in FIG. 1 of said application. The lands of these rolls are wiper by resin-applying felts. The final pair of rolls replaces the idler roller 218 in FIG. 5 of said application and is placed lower than that roller so that the path leading through the carbon applicator chamber and into the conveyor-assembler section is at an angle of only about 10 below the horizontal. The applicator chamber with agitated bed of activated carbon particles and incoming carbon stream is placed across the path of the filter strip between the final pair of rolls men tioned above and the inserter wheel 220. To provide space for the elements needed for the present invention, it is necessary to increase the distance between the printerembosser train pictured in FIG. 5 of the drawing of said application and the conveyor-assembler section beginning at wheel 220.

I claim:

1. A method for forming a continuous tubular cigarette filter rod comprised of at least two interfitting longitudinal parti-tubular sections each having a repeating pattern of inegral transverse smoke barriers and supporting ribs thereon which comprises advancing a continuous strip of moldable material longitudinally into a rotating forming wheel having separate endless molding grooves extending around the periphery thereof with the strip covering said molding grooves, said molding grooves having each a shape adapted to shape one of said sections, drawing the strip into said molding groove to shape the respective parti-tubular sections therein, removing the shaped strip from the forming wheel and severing it longitudinally into the respective sections, thereafter bringing the shaped sections into registering assembly with the smoke barriers in one section axially spaced relative to the smoke barriers in the other section and aligned with a supporting rib in said other section while simultaneously feeding a continuous strip of filter material longitudinally intermediate the shaped sections as they are brought into registering assembly and applying to selected portions of the two faces of said filter material an adhesive material which remains tacky for a period of at least one second and thereafter applying granular solid adsorbent particles to said adhesive coated filter surfaces.

References Cited UNITED STATES PATENTS 2,912,043 11/1959 Bargholtz et al 156-292 3,006,346 10/1961 Golding 131-265 3,323,274 6/1967 Justus 156-292 CARL D. QUARFORTH, Primary Examiner HARVEY E. BEHREND, Assistant Examiner US. Cl. X.R. 13126S 

